Gliding elements forming a gliding surface have been used for a long time, usually in down-slopes of ski jumping hills and at the sides of in-run ski tracks uphill. Gliding elements of relatively small size have been arranged side by side and one after another in a way that the abutments of the gliding elements are overlapped to achieve an integrated gliding surface formed by the gliding elements. The gliding properties of the gliding surface correspond very well to the properties of snow, which is important for ski jumping similar to winter conditions also in the summer.
The gliding elements are attached to a framework, such as a metal net, mounted in the slope and thus placed directly below the gliding surface. Consequently, the risk is that if the ski-jumper falls the fibres forming the gliding unit turn away and the ski-jumper hurt himself when falling onto the exposed metal net.
To eliminate this problem, an improved gliding unit is presented in the Patent Publication FI-71065.
The solution presented in the publication is characterized in that a bottom plate, either uniform or formed of separate strips, corresponding substantially to the size of the gliding element is attached to the same abutment below a plastic mat. As an advantageous embodiment, also a profile bottom plate is presented in the publication. With the profile form, it was attempted to make the gliding element flexible in order to avoid the need for using an additional flexible layer, usually of cellular plastic, commonly used underneath the metal net. In spite of its advantageous principle, this solution has obviously not convinced the users, because its application in practice has remained insignificant.
Particularly when equipped with a uniform bottom plate, the embodiment described above might, in principle, function in a reasonable way. Nevertheless, this embodiment still has the disadvantage typical of conventional gliding elements that the length of the gliding unit of the gliding element substantially corresponds to the total length of the gliding element. However, relatively long fibres do not function satisfactorily, because in practice they are placed and returned into the longitudinal direction at random. Consequently, after the previous jump, the coating may have openings with uncovered metal net or bottom plate.
The problem described above can be overcome by placing several gliding elements on top of each other in a way that there are several layers of gliding units. In the embodiment presented in the Finnish Patent Publication mentioned above, it is possible to make the total length of the gliding element correspondingly shorter. However, such arrangements are not economically advantageous, because the covering must thus be formed of a relatively large number of gliding elements.
Further, the profile bottom plate used in the embodiment of the above patent publication is not particularly advantageous, because it has a corrugated form in the transverse direction which produces a "nubbly" coating and thus may hamper the return of the fibres into the longitudinal direction.